(a) Field of the Invention
The present invention relates to a chargeable-and-dischargeable power supply system and, more particularly, relates to the power supply system controlling an electrical power of the power supply system constituted by a plurality of battery cell sections connected in series with one another (in a multiplex connection form) and having a function to detect (charge) states of charging sections (for example, secondary cells) of the respective battery cell sections.
(b) Description of the Related Art
In an electric vehicle which travels using an electric motor, a hybrid vehicle (hereinafter, also referred to as an HEV vehicle) which travels using both of an engine and the electric motor, or a fuel cell automotive vehicle, a secondary cell such as a Ni-MH (Nickel Metal Hydride) battery or Lithium battery is a unit cell and a battery cell group in which a plurality of unit cells are connected in a multiplex connection form or a large-capacity capacitor is used for the power supply of the electric motor. The battery cell group or the large-capacity capacitor is used for the power supply of the electric motor. The battery cell group or the large-capacity capacitor serves to supply an electric power (namely, to discharge) to the electric motor or other systems at a time of a vehicular start, during a traveling, and during a start for a vehicular stop and serves to store or charge using a regeneration action of the electric motor. It is known that the battery cell group discharges the electric power by a large amount of power or if the battery cell group charges the electric power by the large amount of power, voltages between the respective cells or remaining capacities (charge quantities) therebetween are different from the respective battery cells. Hence, an excessive charge or excessive discharge state often occurs. If such an excessive charge state or excessive discharge state occurs, an unfavorable state occurs such as a liquid leakage, an abnormal heat generation, or a shortening of a cell life. Hence, it is necessary to establish a technique to detect voltages of the unit cells of the battery cell group with a high accuracy and in safety. To achieve this technique, input and output controls of the power of the battery cell group or the capacitor and a protection function (excessive charge protection or excessive discharge protection) are carried out.
Ordinarily, cell state detection and protection sections to detect the states of the unit cells of the battery cell group or the state of the capacitor (hereinafter, CC sections) perform controls and detections using the battery cell group power supply or capacitor (large power side) power supply. A section (hereinafter, also called a BC section) which performs the input-and-output controls of the power of the battery cell group or the capacitor and the protection of the battery cell group or the capacitor performs the input-and-output control and the protection using an on-board battery ordinarily mounted in the vehicle (a battery of 12 volts). Therefore, the power supply is different between that for the CC sections and that for the BC section. To perform the information (signal) transmission or reception between the CC sections and the BC section, a communication is carried out with an electrical isolation provided. This is described in a Japanese Patent Application First Publication (tokkai) No. Heisei 8-339829 (title: a monitor device for the battery cell group) published on Dec. 24, 1996 and a Japanese Patent No. 3545367 issued on Apr. 16, 2004 (title: voltage detection apparatus for the battery cell group).